Binder jetting is an additive manufacturing process in which a part is fabricated layer-by-layer using inkjet technology to selectively dispense binder into powder layers in a designated area. The approach gives this process significant advantages over other additive manufacturing processes such as lower cost, capability to print in a wide range of materials, and little to no heat applied. Although binder jetting has many advantages and has been successful implemented in various industries its overall rate of adoption is slow compared to other processes. This is largely due to poor mechanical properties and consistency in printing which stems from a poor understanding of the interaction between the binder droplets and the powder bed. This is evident as print parameters for new machines and new materials are primarily determined by trial and error. The purpose of this thesis is to report the impact of various inkjet print parameters and humidity on the printing process in binder jetting. The binder/powder interaction is complex and highly dynamic where picoliter-sized droplets impact the powder bed at velocities of 1-10 m/s. Current methods of predicting this interaction assume that it is based only on binder and powder properties. This work studies the impact of inkjet printing parameters that are often overlooked with these assumptions. The impact of droplet velocity, droplet spacing, and droplet inter-arrival time was evaluated based on single line formation and effective saturation levels when printed into various powder material and sizes. Higher droplet velocities were found to decrease effective saturation with larger droplets (92-212 pl). However, droplet velocity had a negligible impact on saturation when printing with smaller droplets from 30 m orifice (29-65 pl). Line formation was dependent on both droplet inter-arrival time and droplet spacing. Max droplet spacing correlated to the square root of inter-arrival time. These results can guide selection of printing parameters that maximize build rates and reduce defects in printed parts. As the binder/powder interaction is difficult to observe and often line formation has been used as a method of observation. However, no report relating line formation to full layer parts exists. Optimal parameters determined in line printing are used for full feature parts. In addition, the impact of ambient humidity on the printing process is studied. The direct use of parameters optimized for line printing in printing a part was shown to be ineffective. When droplet spacing, line spacing, and layer thicknesses are comparable, single and multiple layers can be formed. Over short exposure periods of powder to ambient humidity produces negligible difference however, extended exposure periods significantly reduce the saturation and increase part size. Surface roughness is identified as a possible source of printing defects. Surface roughness increases significantly when printing the first layer but decreases with successive layers. This demonstrates a strong interaction between layers. The surface roughness and effective saturation was insensitive to line and droplet spacing below 60 m. Steam powder conditioning reduces sensitivity of both surface roughness and saturation to printing parameters but causes bleeding beyond the part boundaries. Further research should include improved methods of predicting ideal printing parameters and connecting it based on geometry and parts size. Further research is needed to confirm impact of surface roughness on defects in binder jetting parts. Development of methods to control spread of binder in premoistened powder to take advantage of its potential.

Incipient motion criterion in sediment transport is very important, as it defines the flow condition that initiates sediment motion, and is also frequently employed in models to predict the sediment transport at higher flow conditions as well. In turbulent flows, even a reasonably accurate definition of incipient motion condition becomes very difficult due to the random nature of the turbulent process, which is responsible for sediment motion under incipient conditions. This work investigates two aspects, both of which apply to incipient sediment transport conditions. The first one deals with the role of turbulence in initiating sediment motion. The second part deals with the nature of sediment-fluid interaction for more general and complex flows where the number of sediment particles that form the rough surface is varied. The first part of this work that investigates the role of turbulence in initiating sediment motion, uses a video camera to simultaneously monitor and record the sediment (glass ball) motion and corresponding fluid velocity events measured by a three-component laser Doppler Velocimeter (LDV). The results of the single ball experiment revealed that the number of LDV flow measurements increase dramatically (more than four folds) just prior to the ball motion. The fluid mean velocity and its root-mean-square (rms) values also are significantly higher than the values that correspond to the flow conditions that yield no ball motion. The second part of the work, investigation of the fluid-sediment interaction, includes five tests with varying number of sediment particles. In order to understand the nature and extent of fluid-solid interaction, velocity profile measurements using the 3-D laser system were carried out at three locations for each of these five cases. Plots of mean velocities, rms quantities located the universal layer at about 1.5 ball diameters above the porous bed. However, at higher sediment particle concentrations, this distance reduced and the beginning of the universal layer approached the top of the porous bed. / Ph. D.

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Pipes in water distribution systems may change as they age. The accumulation of corrosion byproducts and suspended particles on the inside wall of aged pipes can increase pipe roughness and reduce pipe diameter. To quantify the hydraulic effects of irregular accumulation on the pipe walls, eleven aged pipes ranging in diameter from 0.020-m (0.75-in) to 0.100-m (4-in) and with varying degrees of turberculation were located and subjected to laboratory testing. The laboratory test results were used to determine a relationship between pipe diameter reduction and Hazen-Williams C. This relationship, combined with a manipulation of the Hazen-Williams equation, provided a simple and direct method for correcting the diameters of aged pipes in distribution models. Using EPANET 2, the importance of correcting pipe diameters when modeling water distribution systems containing aged pipes was investigated. Correcting the pipe diameters in the sample network reduced the modeled water age by up to 10% and changed the pattern of fluctuating water age that occurred as waters with different sources moved through the pipe network. In addition, two of the aforementioned aged pipes with diameters of 0.025-m (1-in) and 0.050-m (2-in) were modeled using Reynolds-Averaged Navier-Stokes (RANS) turbulence modeling. Flow was computed at Reynolds numbers ranging from 6700 to 31,000 using three turbulence models including a 4-equation v2-f model, and 2-equation realizable k-e; and k-ω models. In comparing the RANS results to the laboratory testing, the v2-f model was found to be most accurate, producing Darcy-Weisbach friction factors from 5% higher to 15% lower than laboratory-obtained values. The capability of RANS modeling to provide a detailed characterization of the flow in aged pipes was demonstrated. Large eddy simulation (LES) was also performed on a single 0.050-m (2-in) pipe at a Reynolds number of 6800. The Darcy-Weisbach friction factor calculated using LES was 20% less than obtained from experimental tests. Roughness elements smaller than the grid scale and deficiencies in the subgrid-scale model at modeling the complex three-dimensional flow structures due to the irregular pipe boundary were identified as likely sources of error. Even so, the utility of LES for describing complex flows was established.

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Electromagnetic scattering from a rough two dimensional homogeneous scatterer has been computationally modeled. The scatterer is intended to simulate reflection from a two interface multilayer. The rough scatterer was created from Gaussian random points centered about an ideal interface. The points were connected with a third order spline interpolant which accounts for correlation between neighboring surface atoms. The scalar electric field integral equation (EFIE) and magnetic field integral equation (MFIE) were solved using the Nystrom method to obtain the reflected intensity as a function of observation angle. Verification of the accuracy of the code was obtained by means of comparison with well-known analytic solutions and approximations. The predicted Nevot-Croce factor drop in reflectance was found to be in general agreement with the computed decrease in reflectance due to surface roughness. However, an angle dependent difference was also noticed, indicating the Nevot-Croce factor might need revision. The code is being modified to run on a supercomputing cluster where longer, more realistic surfaces can be analyzed to determine whether an improved roughness correction factor is needed.